Stabilizers for watercraft, in particular fin stabilizers, may be used both for stabilizing watercraft while underway (while operating or traveling) as well as for stabilizing watercraft that are anchored or moving at low speed during “pre-anchor” operation. The requirements for stabilizing a watercraft moving at a relatively high speed, however, are different than (and conflict with) the requirements for stabilizing a watercraft moving slowly or not at all. Stabilizer fins optimized for driving/traveling operation preferably have a wide span and a short chord length relative thereto. Lifting forces for stabilizing the watercraft are produced by the oncoming/incident flow of water during travel and the angle of attack of the fin stabilizers. To minimize the required drive torque, (the torque required to maintain or change the angle of attack) the axis of rotation should be located in the vicinity of the center of lift of the fin stabilizer.
For pre-anchor stabilizing, on the other hand, there is no or negligible oncoming flow with respect to the stabilizer fins. Therefore, forces for counteracting a rolling movement must be generated by the fin stabilizers themselves, that is by moving the stabilizer fins to displace water and/or create a flow of water around the moved stabilizer fin. For a fin having approximately the same span width, stabilizer fins used for pre-anchor stabilizing should have a large chord length and an axis of rotation closer to the nose of the stabilizer fin. High drive torques are required in order to allow stabilizers adapted for pre-anchor operation to also be used to effectively counteract rolling movements of the watercraft in driving operation. Due to the large stabilizer fin and the requirement for a powerful drive, these stabilizer systems are heavy, consume a relatively large amount of power and occupy a large space in the watercraft. Furthermore, when designing fin stabilizers, a compromise must be made between optimizing the stabilizer for driving operation and optimizing the stabilizer for pre-anchor operation.
A fin including a variably adjustable outer contour is disclosed in U.S. Pat. No. 5,367,970 A. Control wires are integrated in the fin which change the curvature of the fin when their lengths change. The change in length is regulated by a control system.
A fin stabilizer for stabilizing a watercraft is known from DE 102011005313 B3. This stabilizer includes a main fin that is pivotable by a watercraft-side fin drive and a tail fin that is movably supported on the main fin. The fin stabilizer includes a locking device that actively regulates the pivoting of the tail fin. In pre-anchor operation the locking device blocks a possible pivoting movement of the tail fin and thereby increases the surface of the stabilizer fin. In driving operation the locking device is switched to free movement (unlocked) and makes possible a free pivoting movement of the tail fin so that the surface of the stabilizer fin is reduced.
These known concepts provide for a more effective stabilizing of watercraft than one-part stabilizer fins, in particular by adjusting the effective surface area of the stabilizer fins. However, in both cases an active regulating device is required to select between pre-anchor and driving operation states. Furthermore in DE 102011005313 the locking device includes of a variety of mechanical or hydraulic components.
U.S. Pat. No. 2,151,836 A discloses a boat including collecting surfaces for wave shocks as well as support surfaces that reduce the tendency of the bow to sink. Publication DE 60 2005 004 944 T2 discloses an active roll-stabilization system for ships. Stabilizing fins for damping the longitudinal movement of keel yachts are known from publication DE 39 39 435 A1.